Electrical resistance element



Patented Jan. 9, 1945 ELECTRICAL RESISTANCE ELEMENT Harry I. Heimberger, Rolls, Mo., asslgnor, by decree oi. distribution, to Pansye M. Helmberger Application July 29, 1943, Serial No. 496,530

2 Claims.

This invention relates to compound resistance wires for use in electrical instruments.

The desirable characteristics oi resistance wires are well known, namely, high electrical resistance; low thermal E. M. F. against copper; resistance to atmospheric corrosion; stability of resistance; capability of drawing into line wire and ease of manufacture, which insures reproducibility.

The art is familiar with alloys of manganese, copper and nickel which have been used for this purpose under various trade names, such as Constantan and Manganin. These alloys have speciiic electrical resistance oi! the order of 100 microhms per centimeter cubed. They are moderately good in other respects. More recently there have been introduced alloys of silver, manganese and tin with specific resistances of approximately 75 microhms per centimeter cubed. Finally, alloys of copper and manganese and oi copper, manganese and nickel made'with electrolytic manganese have been described. These alloys, containing around 65% manganese, have specific electrical resistances as high as 195 microhms per centimeter cubed. They have a very low temperature coemcient of electrical resistance and low thermal electromotive force against copper.

They are, however, not as corrosion resistant as desired.

In the drawing Figure 1 shows a graph of the silver-manganese alloys used in the sheath of my resistor, and Figure 2 shows a graph the copper-manganese alloys used in the core of my resistor.

In my invention I make use of the desirable high resistances of the high manganese alloys in combination with silver alloys having relative- 1y high electrical-eresistance low temperature coefllcient and high'icorrosion resistance. Basically, I start with alloys of manganese and copper, the electrical properties of which are represented in Figure No. 2. I then develop a silver alloy sheath having suitable electrical characteristics, so that a wire of the manganese-copper alloy, sheathed with a silver alloy, will have substantially zero temperature coefllcient oi electrical resistance and very low thermal electromotive force against copper.

For example, I take an alloy of copper and bout 1'16 microhms per centimeter cubed.-

Temperature coeflicient-about --.52x10- Thermal electromotive force-about .45 millivolt against copper at 100 C.

I sheath this with an alloy of silver and manganese selected from the electrical data on silvermanganese alloys in Figure No. 1. These data, like those on manganese-copper alloys, are for cold drawn wires, except where noted,

It will be seen that with an alloy of approximately 18% manganese the properties are:

Riesistanceabout microhms.

Temperature coeflicientabout +7.0x10- Thermal electromotive Iorceabout +415 millivolt against copper at C.

Resistance-about 161.37 microhms per centimeter cubed.

Temperature coeflicient-substantially zero.

Thermal electromotive force-against copper substantially zero.

The silver-manganese alloy is highly corrosion resistant and very ductile and easily worked.

It will be obvious to those skilled in the art that many compound elements can be worked out using silver-manganese alloys as sheaths for copper-manganese alloys. The silver-manganese alloys can be alloyed with relatively small percentages of other elements, such as tin, and the manganese-copper alloys can be alloyed with other elements, such as nickel or zinc, without departing from my invention, which resides in using a sheath of corrosion resisting silver alloy on a high resistance manganese alloy so as to obtain an electrical resistance wire having high electrical resistance, high corrosion resistance, low temperature coefllcient and low thermal electromotive force against copper.

Heat treatment may be resorted to, in order to vary the properties of one or both of the alloys in the compound resistance element without departing from my invention.

In making the compound elements of my invention, methods known in the art may be used, but I prefer to cast the high manganese alloy in the form of a cylinder and, after cleaning thoroughly, cast around it the silver alloy. The whole is then drawn to any desired size of wire.

The sheath of a ductile silver alloy aids in drawingiinewireeveniithealloyotthe coreislees ductile.

Compound forms, other than wire, can be used, such as lamellar tapes. without departing from my invention.

sheath of an alloy 0! silver and manganese containing at least percent silver and having a positive temperature coeiiicient of electrical nesistance.

2. A compound resistance element having a core of a manganese copper alloy containingabout 00 percent manganese and a sheath oi manganese silver alloy containing about 18 percent silver. the sheath having approximately 2.5 percent oi! nickel 2-60, said alloy having a negative temperathe cross sectional area 01 the compound wire.

ture coemcient oi electrical resistance and a 

